As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for batteries has also sharply increased as an energy source for the mobile devices. Accordingly, much research on batteries satisfying various needs has been carried out.
In terms of the shape of batteries, the demand for prismatic secondary batteries or pouch-shaped secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for batteries, the demand for lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, having a high energy density, a high discharge voltage, and a high output stability, is very high.
Furthermore, secondary batteries may be classified based on the construction of an electrode assembly having a cathode/separator/anode structure. For example, the electrode assembly may be constructed in a jelly-roll (winding) type structure in which long-sheet type cathodes and anodes are wound while separators are disposed respectively between the cathodes and the anodes, a stacking type structure in which pluralities of cathodes and anodes having a predetermined size are sequentially stacked while separators are disposed respectively between the cathodes and the anodes, or a stacking/folding type structure in which pluralities of cathodes and anodes having a predetermined size are sequentially stacked while separators are disposed respectively between the cathodes and the anodes to constitute a bi-cell or a full-cell, and then the bi-cell or the full-cell is wound.
Recently, much interest has been taken in a pouch-shaped battery constructed in a structure in which such a stacking or stacking/folding type electrode assembly is mounted in a pouch-shaped battery case made of an aluminum laminate sheet because of low manufacturing costs, light weight, and easy modification in shape. As a result, the use of the pouch-shaped battery has gradually increased.
FIG. 1 is an exploded perspective view typically illustrating the general structure of a conventional representative pouch-shaped secondary battery.
Referring to FIG. 1, the pouch-shaped secondary battery 10 includes an electrode assembly 30, pluralities of electrode tabs 40 and 50 extending from the electrode assembly 30, electrode leads 60 and 70 welded to the electrode tabs 40 and 50, respectively, and a battery case 20 for receiving the electrode assembly 30.
The electrode assembly 30 is a power generating element comprising cathodes and anodes sequentially stacked while separators are disposed respectively between the cathodes and the anodes. The electrode assembly 30 is constructed in a stacking structure or a stacking/folding structure. The electrode tabs 40 and 50 extend from corresponding electrode plates of the electrode assembly 30. The electrode leads 60 and 70 are electrically connected to the electrode tabs 40 and 50 extending from the corresponding electrode plates of the electrode assembly 30, respectively, for example, by welding. The electrode leads 60 and 70 are partially exposed to the outside of the battery case 20. To the upper and lower surfaces of the electrode leads 60 and 70 are partially attached insulative films 80 for improving sealability between the battery case 20 and the electrode leads 60 and 70 and, at the same time, for securing electrical insulation between the battery case 20 and the electrode leads 60 and 70.
The battery case 20 is made of an aluminum laminate sheet. The battery case 20 has a space, i.e., a receiving part, defined therein for receiving the electrode assembly 30. The battery case 20 is formed generally in the shape of a pouch. In the case that the electrode assembly 30 is a stacking type electrode assembly as shown in FIG. 1, the inner upper end of the battery case 20 is spaced apart from the electrode assembly 30 such that the plurality of cathode tabs 40 and the plurality of anode tabs 50 can be coupled to the electrode leads 60 and 70, respectively. Also, the receiving part of the battery case 20, in which the electrode assembly 30 is received, is generally formed by a deep drawing process. As a result, predetermined inclination and curvature are formed at the side of the receiving part, and therefore, a predetermined space is defined between the outer surface of the electrode assembly 30 and the side of the receiving part. The space is gradually increased by the movement of the electrode assembly in the receiving part of the battery case 20 due to external impact applied to the battery case 20, and the electrode tabs 40 and 50 and the electrode leads 60 and 70 are deviated from their original positions due to the movement of the electrode assembly 30.
FIG. 2 is an enlarged view, in section, illustrating the inner upper end of the battery case of the secondary battery shown in FIG. 1, in which the cathode tabs are coupled to each other in a concentrated state and connected to the cathode lead, and FIG. 3 is a front see-through view illustrating the secondary battery of FIG. 1 in an assembled state.
Referring to these drawings, the plurality of cathode tabs 40, which extend from cathode collectors 41 of the electrode assembly 30, are connected to one end of the cathode lead 60, for example, in the form of a welded bunch constituted by integrally combining the cathode tabs 40 with each other by welding. The cathode lead 60 is sealed by the battery case 20 while the other end 61 of the cathode lead 60 is exposed to the outside of the battery case 20. Since the plurality of cathode tabs 40 are integrally combined with each other to constitute the welded bunch, the inner upper end of the battery case 20 is spaced a predetermined distance from the upper end surface of the electrode assembly 30, and the cathode tabs 40 combined in the form of the welded bunch are bent approximately in the shape of V. Accordingly, the coupling regions between the electrode tabs and the corresponding electrode leads may be referred to as “V-form regions.”
However, such V-form regions have a problem in the aspect of safety of the battery. Specifically, when the battery drops with the upper end of the battery, i.e., the cathode lead 60 of the battery, down, or an external physical force is applied to the upper end of the battery, the electrode assembly 30 moves toward the inner upper end of the battery case 20, or the upper end of the battery case 20 is crushed. As a result, the anode of the electrode assembly 30 is brought into contact with the cathode tabs 42 or the cathode lead 60, and therefore, short circuits may occur inside the battery. Consequently, the safety of the battery is greatly lowered.
In this connection, Japanese Patent Application Publication No. 2000-200584 discloses a technology for forming pluralities of grooves and flat parts along the side of a receiving part of a battery case, constructed in a trapezoidal shape when viewing the vertical section of the battery case, to restrain the movement of a jelly-roll type electrode assembly, having a semicircular section, in the receiving part of the battery case. However, the disclosed technology has a drawback in that the plurality of grooves, having relatively small height, must be formed at the side of the receiving part of the battery case, and therefore, it is difficult to form the grooves. Also, the installation of the electrode assembly in the receiving part is difficult due to the grooves formed at the side of the receiving part along the region adjacent to the opening, and, the grooves may be deformed during the installation of the electrode assembly in the receiving part.
Furthermore, the inventors of the present invention have found that, in the above-described structure, the electrode tabs are in partial contact with the grooves at the upper end of the receiving part, having V-form regions for the coupling between the electrode tabs and the electrode leads, and therefore, the electrode tabs are damaged. Also, when a stacking or stacking/folding type electrode assembly, having a rectangular section, is mounted in the battery case constructed as described above, the grooves are further deformed, when an external impact is applied to the secondary battery, whereby the reliability of the secondary battery is lowered.
Consequently, there is a high necessity for a technology that is capable of easily deforming the receiving part of the battery case, easily mounting the electrode assembly in the receiving part of the battery case, and preventing the occurrence of a short circuit of the secondary battery due to the movement of the electrode assembly.